1. Field of the Invention
The present invention relates to a technology for displaying information by supplying electric power converted by using thermoelectric transduction.
2. Description of the Related Art
Recently, an information display apparatus as a substitute for paper or an electronic device, such as electronic paper, has become a subject of attention. Electronic paper is a display device that is formed in thickness of a few tenth of a millimeter, and capable to display and to delete data thereon through an electrical process, and can be carried by a user while retaining information thereon similarly to paper. Moreover, because electronic paper consumes electric power only when changing screen contents, the electronic paper can maintain a state that image data is displayed thereon even after the power is turned off, thereby drastically reducing power consumption.
When rewriting screen data or deleting image data, electronic paper requires electric power as described above, so that the electronic paper is supplied with electric power by installing thereon a battery or being connected to an external power source.
In addition to a battery, electronic paper using a solar cell as a power supply source is proposed. For example, Japanese Patent Application Laid-open No. 2004-317700 discloses an example of electronic paper equipped with a transparent solar cell instead of a battery.
However, after image data is once displayed on electronic paper, if a battery becomes exhausted or a connection to an external power source is canceled, electric power is not supplied to the electronic paper, consequently, the electronic paper is mechanically to maintain a state that the image data is displayed thereon. When display of the image data is maintained in this way, there is a possibility that someone around the user may easily peep at the image data displayed on the electronic paper, therefore, the electronic paper cannot deal with confidential information, and has to limit contents of information to be displayed. It is also difficult to limit display of image data only to a user who is involved in confidential information.
To ensure the confidentiality of image data displayed on electronic paper, it needs to rewrite or delete the displayed image data by supplying electric power to the electronic paper. However, if a battery is installed on electronic paper, work of charging the battery is required, or if an external power source is connected to the electronic paper, work of connecting the external power source is required, any of which is inconvenient. Moreover, if a battery is installed on electronic paper, the electronic paper becomes heavier and larger, resulting in a problem of poor portability. Furthermore, when frequently rewriting image data, electronic paper has to be equipped with a battery having a capacity adequate for rewriting image data, as a result, if an installed battery becomes large, the electronic paper becomes larger, so that its portability becomes poorer.
Electronic paper equipped with a transparent solar cell as disclosed in the patent document No. 2004-317700 tends to be affected by environmental conditions, so that when using it indoors or at night, electric power cannot be supplied, resulting in a poor convenience.